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How can I mock a class which uses a SLF4J Log4J Logger?

I try to Mock a Class which instantiates a DatabaseConnection via Hibernate over an other Class, but I get errors of the SLF4J Error Factory in the Class, but I want the Logger to run in this Test to. How could I fix this to Mock the class and then instantiate the List and Logger successful?
I tried to Mock the Class (Ingredientadminsitration) and then this:
PowerMockito.mockStatic(LoggerFactory.class);
when(LoggerFactory.getLogger(any(Class.class))).
thenReturn(loggerMock);
Ingredientadministration.java
#Slf4j
public class Ingredientsadministration {
private ObservableList<Ingredient> zutaten;
private SQLConnection sqlConnection;
private static Ingredientsadministration ingredientsadministration;
private Logger logger;
private Ingredientsadministration() {
logger = LoggerFactory.getLogger(this.getClass());
connectToDB();
zutaten = FXCollections.observableArrayList(sqlConnection.getZutaten());
}
public static Ingredientsadministration getInstance() {
if (ingredientsadministration == null) {
ingredientsadministration = new Ingredientsadministration();
}
return ingredientsadministration;
}
MySQLHibernate.java
#Slf4j
public class MySQLConnectHibernate implements SQLConnection {
private static SessionFactory sessionFactory;
private Session session;
private Logger logger;
private static MySQLConnectHibernate entity;
private MySQLConnectHibernate() throws ServiceException {
logger = LoggerFactory.getLogger(this.getClass());
setup();
}
public static MySQLConnectHibernate getInstance() {
if (entity == null) {
entity = new MySQLConnectHibernate();
}
return entity;
}
private void setup() throws ServiceException {
if (sessionFactory == null) {
sessionFactory = new Configuration().configure().buildSessionFactory();
logger.debug("Create new SessionFactory={}.", sessionFactory);
}
}

I suggest you want to test if the specific message is logged? First of all if you use #sl4j you don't have to instantiate a logger by yourself. Lombok will do this for you (log.debug(..)) should be used then. You can receive the logger in your test via LoggerFactory.getLogger(SomeClass.class); You can attache a mocked appender and check if the wanted log entry was written to your mocked appender. Here's a simple example: https://dzone.com/articles/unit-testing-asserting-line

Dagger 2 How to solve constructor dependency

I am an Android developer and trying to learn Dagger2. I have gone through some tutorials and got some basic understanding. I developed a basic java app using Dagger2. And below is my app code.
Logger.java: Logger is simple java class which will print logs with some tag.
public class Logger {
private String tag;
#Inject
public Logger(String tag) {
this.tag = tag;
}
public void log(String msg) {
System.out.println(tag + "::" + msg);
}
}
InvertNumber.java: It will invert the passed number and prints log using Logger
public class InvertNumber {
private Logger logger;
#Inject
public InvertNumber(Logger logger) {
this.logger = logger;
}
public void invert(int i) {
logger.log("Inverted value is " + (i * -1));
}
}
Now I added Dagger2 depency classes (Module and component) like below
#Module
public class NumberModule {
private String tag;
public NumberModule(String tag) {
this.tag = tag;
}
#Provides
Logger provideLogger(){
Logger logger = new Logger(tag);
return logger;
}
#Provides
InvertNumber provideTempManager(Logger logger){
return new InvertNumber(logger);
}
}
#Component(modules = NumberModule.class)
public interface NumberComponent {
InvertNumber getInvertNumber();
}
Now below is my main method.
public static void main(String[] args) {
NumberComponent numberComponent = DaggerNumberComponent.builder()
.numberModule(new NumberModule("MyMain"))
.build();
InvertNumber invertNumber = numberComponent.getInvertNumber();
invertNumber.invert(10);
}
To print logs in console, I have to provide tag to the logger. For this I am creating instance of NumberModule class and passing to NumberComponent builder.
Now my questions are:
Is this correct way to pass tag using NumberModule instance
If it is correct, according to DI concept, it is not encouraged to
use new operator to create objects (new NumberModule())
If the above code is wrong, what is the correct way?

Your way of solving problem is right, but there is one more using #Component.Buidler. (please, note that in your case #Inject annotation in Logger and InvertNumber constructor not working - you call them by hand).
Rewrite dagger stuff like that
#Module
public class NumberModule {
#Inject
public NumberModule() {}
#Provides
Logger provideLogger(#Named("logger_tag") String tag){
Logger logger = new Logger(tag);
return logger;
}
#Provides
InvertNumber provideTempManager(Logger logger){
return new InvertNumber(logger);
}
}
#Component(modules = NumberModule.class)
public interface NumberComponent {
InvertNumber getInvertNumber();
#Component.Builder
interface Builder {
#BindsInstance
Builder loggerTag(#Named("logger_tag") String tag);
NumberComponent build();
}
}
and use it
NumberComponent numberComponent = DaggerNumberComponent.builder()
.loggerTag("MyMain")
.build();
To allow dagger create Logger and InvertNumber for you (not manually calling their constructors), you need interfaces for each of them.

Make the "LOGGER" logger private static final error is thrown for interface in SonarQube

By default Java Interface doesn't allow private static final members. But in SonarQube, Make the "LOGGER" logger private static final error is thrown for interface.
Any specific reason for this?
Example:
public interface UserPropUtil {
static final Logger LOGGER=Logger.getLogger(UserPropUtil.class.getName());
static String getUserProp(String key, String defaultValue) {
Userprop toReturn=null;
try {
toReturn= getUserProp(key);
} catch (Exception e) {
LOGGER.severe(e.getMessage());
}
return toReturn;
}
}

Static Field as Null when mocking Enums with PowerMock

I have written a Thread Pool and I am not able to write the Junits(PowerMock) for that class.
public enum ThreadPool {
INSTANCE;
private static final String THREAD_POOL_SIZE = "threadpool.objectlevel.size";
private static TPropertyReader PROP_READER = new PropertyReader();
private final ExecutorService executorService;
private static final ILogger LOGGER = LoggerFactory
.getLogger(ReportExecutorObjectLevelThreadPool.class.getName());
ThreadPool() {
loadProperties();
int no_of_threads = getThreadPoolSize();
executorService = Executors.newFixedThreadPool(no_of_threads);
}
public void submitTask(Runnable task) {
executorService.execute(task);
}
private static void loadProperties() {
try {
PROP_READER.loadProperties("Dummy");
} catch (final OODSystemException e) {
LOGGER.severe("Loading properties for app failed!");
}
}
private int getThreadPoolSize() {
return Integer.valueOf(PROP_READER
.getProperty(THREAD_POOL_SIZE));
}
}
While Mocking this class I am getting NullPointerException in the line PROP_READER.loadProperties("DUMMY");
My Test Case is:-
PowerMockito.whenNew(PropertyReader.class).withNoArguments().thenReturn(mockPropertyReader);
PowerMockito.doNothing().when( mockPropertyReader,"loadProperties",anyString());
mockStatic(ThreadPool.class);

First you need to set your internal state of your enum as enum is final class
and the instance of an enum will be load on class loading
ThreadPool mockInstance = mock(ThreadPool .class);
Whitebox.setInternalState(ThreadPool.class, "INSTANCE", mockInstance);
then
PowerMockito.mockStatic(ThreadPool .class);
and then mocking
doNothing().when(mockInstance).loadProperties(any(String.class));
do not forget adding the following annotation to the test
#RunWith(PowerMockRunner.class)
#PrepareForTest({ThreadPool.class})
if it still not working you need to see which more member of the class you need to set in the internal state

Java logger that automatically determines caller's class name

public static Logger getLogger() {
final Throwable t = new Throwable();
final StackTraceElement methodCaller = t.getStackTrace()[1];
final Logger logger = Logger.getLogger(methodCaller.getClassName());
logger.setLevel(ResourceManager.LOGLEVEL);
return logger;
}
This method would return a logger that knows the class it's logging for.
Any ideas against it?
Many years later: https://github.com/yanchenko/droidparts/blob/master/droidparts/src/org/droidparts/util/L.java

The MethodHandles class (as of Java 7) includes a Lookup class that, from a static context, can find and return the name of the current class. Consider the following example:
import java.lang.invoke.MethodHandles;
public class Main {
private static final Class clazz = MethodHandles.lookup().lookupClass();
private static final String CLASSNAME = clazz.getSimpleName();
public static void main( String args[] ) {
System.out.println( CLASSNAME );
}
}
When run this produces:
Main
For a logger, you could use:
private static Logger LOGGER =
Logger.getLogger(MethodHandles.lookup().lookupClass().getSimpleName());

Creating a stack trace is a relatively slow operation. Your caller already knows what class and method it is in, so the effort is wasted. This aspect of your solution is inefficient.
Even if you use static class information, you should not fetch the Logger again for each message. From the author of Log4j,Ceki Gülcü:
The most common error in wrapper classes is the invocation of the Logger.getLogger method on each log request. This is guaranteed to wreak havoc on your application's performance. Really!!!
This is the conventional, efficient idiom for getting a Logger is during class initialization:
private static final Logger log = Logger.getLogger(MyClass.class);
Note that this gives you a separate Logger for each type in a hierarchy. If you come up with a method that invokes getClass() on an instance, you will see messages logged by a base type showing up under the subtype's logger. Maybe this is desirable in some cases, but I find it confusing (and I tend to favor composition over inheritance anyway).
Obviously, using the dynamic type via getClass() will require you to obtain the logger at least once per instance, rather than once per class like the recommended idiom using static type information.

I guess it adds a lot of overhead for every class. Every class has to be 'looked up'. You create new Throwable objects to do that... These throwables don't come for free.

We actually have something quite similar in a LogUtils class. Yes, it's kind of icky, but the advantages are worth it as far as I'm concerned. We wanted to make sure we didn't have any overhead from it being repeatedly called though, so ours (somewhat hackily) ensures that it can ONLY be called from a static initializer context, a la:
private static final Logger LOG = LogUtils.loggerForThisClass();
It will fail if it's invoked from a normal method, or from an instance initializer (i.e. if the 'static' was left off above) to reduce the risk of performance overhead. The method is:
public static Logger loggerForThisClass() {
// We use the third stack element; second is this method, first is .getStackTrace()
StackTraceElement myCaller = Thread.currentThread().getStackTrace()[2];
Assert.equal("<clinit>", myCaller.getMethodName());
return Logger.getLogger(myCaller.getClassName());
}
Anyone who asks what advantage does this have over
= Logger.getLogger(MyClass.class);
has probably never had to deal with someone who copies and pastes that line from somewhere else and forgets to change the class name, leaving you dealing with a class which sends all its stuff to another logger.

Assuming you are keeping static refs to the loggers, here's a standalone static singleton:
public class LoggerUtils extends SecurityManager
{
public static Logger getLogger()
{
String className = new LoggerUtils().getClassName();
Logger logger = Logger.getLogger(className);
return logger;
}
private String getClassName()
{
return getClassContext()[2].getName();
}
}
Usage is nice and clean:
Logger logger = LoggerUtils.getLogger();

For every class that you use this with, you're going to have to look up the Logger anyway, so you might as well just use a static Logger in those classes.
private static final Logger logger = Logger.getLogger(MyClass.class.getName());
Then you just reference that logger when you need to do your log messages. Your method does the same thing that the static Log4J Logger does already so why reinvent the wheel?

A good alternative is to use (one of) the lombok logs annotations :
https://projectlombok.org/features/Log.html
It generate the corresponding log statement with the current class.

Then the best thing is mix of two .
public class LoggerUtil {
public static Level level=Level.ALL;
public static java.util.logging.Logger getLogger() {
final Throwable t = new Throwable();
final StackTraceElement methodCaller = t.getStackTrace()[1];
final java.util.logging.Logger logger = java.util.logging.Logger.getLogger(methodCaller.getClassName());
logger.setLevel(level);
return logger;
}
}
And then in every class:
private static final Logger LOG = LoggerUtil.getLogger();
in code :
LOG.fine("debug that !...");
You get static logger that you can just copy&paste in every class and with no overhead ...
Alaa

From reading through all the other feedback on this site, I created the following for use with Log4j:
package com.edsdev.testapp.util;
import java.util.concurrent.ConcurrentHashMap;
import org.apache.log4j.Level;
import org.apache.log4j.Priority;
public class Logger extends SecurityManager {
private static ConcurrentHashMap<String, org.apache.log4j.Logger> loggerMap = new ConcurrentHashMap<String, org.apache.log4j.Logger>();
public static org.apache.log4j.Logger getLog() {
String className = new Logger().getClassName();
if (!loggerMap.containsKey(className)) {
loggerMap.put(className, org.apache.log4j.Logger.getLogger(className));
}
return loggerMap.get(className);
}
public String getClassName() {
return getClassContext()[3].getName();
}
public static void trace(Object message) {
getLog().trace(message);
}
public static void trace(Object message, Throwable t) {
getLog().trace(message, t);
}
public static boolean isTraceEnabled() {
return getLog().isTraceEnabled();
}
public static void debug(Object message) {
getLog().debug(message);
}
public static void debug(Object message, Throwable t) {
getLog().debug(message, t);
}
public static void error(Object message) {
getLog().error(message);
}
public static void error(Object message, Throwable t) {
getLog().error(message, t);
}
public static void fatal(Object message) {
getLog().fatal(message);
}
public static void fatal(Object message, Throwable t) {
getLog().fatal(message, t);
}
public static void info(Object message) {
getLog().info(message);
}
public static void info(Object message, Throwable t) {
getLog().info(message, t);
}
public static boolean isDebugEnabled() {
return getLog().isDebugEnabled();
}
public static boolean isEnabledFor(Priority level) {
return getLog().isEnabledFor(level);
}
public static boolean isInfoEnabled() {
return getLog().isInfoEnabled();
}
public static void setLevel(Level level) {
getLog().setLevel(level);
}
public static void warn(Object message) {
getLog().warn(message);
}
public static void warn(Object message, Throwable t) {
getLog().warn(message, t);
}
}
Now in your code all you need is
Logger.debug("This is a test");
or
Logger.error("Look what happened Ma!", e);
If you need more exposure to log4j methods, just delegate them from the Logger class listed above.

You could of course just use Log4J with the appropriate pattern layout:
For example, for the class name "org.apache.xyz.SomeClass", the pattern %C{1} will output "SomeClass".
http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/PatternLayout.html

I prefer creating a (static) Logger for each class (with it's explicit class name). I than use the logger as is.

You don't need to create a new Throwable object. You can just call
Thread.currentThread().getStackTrace()[1]

I just have the following line at the beginning of most of my classes.
private static final Logger log =
LoggerFactory.getLogger(new Throwable().getStackTrace()[0].getClassName());
yes there is some overhead the very first time an object of that class is created, but I work mostly in webapps, so adding microseconds onto a 20 second startup isn't really a problem.

Google Flogger logging API supports this e.g.
private static final FluentLogger logger = FluentLogger.forEnclosingClass();
See https://github.com/google/flogger for more details.

A nice way to do this from Java 7 onwards:
private static final Logger logger = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
The logger can be static and that fine.
Here its using the SLF4J API
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
But in principal can be used with any logging framework. If the logger needs a string argument add toString()

Simple and trivial OLD SCHOOL:
Just create your own class and pass there class name, method name + comment (if class /method changed they're refactored automatically Shift+F6)
public class MyLogs {
public static void LOG(String theClass, String theMethod, String theComment) {
Log.d("MY_TAG", "class: " + theClass + " meth : " + theMethod + " comm : " + theComment);
}
}
and just use it anywhere in the app (no context required, no initialzation, no extra libs and no look up) - can be used for any programing language!
MyLogs.LOG("MainActivity", "onCreate", "Hello world");
this will print in your console:
MY_TAG class: MainActivity meth: onCreate comm: Hello world

Why not?
public static Logger getLogger(Object o) {
final Logger logger = Logger.getLogger(o.getClass());
logger.setLevel(ResourceManager.LOGLEVEL);
return logger;
}
And then when you need a logger for a class:
getLogger(this).debug("Some log message")

This mechanism puts in a lot of extra effort at runtime.
If you use Eclipse as your IDE, consider using Log4e. This handy plugin will generate logger declarations for you using your favourite logging framework. A fraction more effort at coding time, but much less work at runtime.

Unless you really need your Logger to be static, you could use
final Logger logger = LoggerFactory.getLogger(getClass());

Please see my static getLogger() implementation (use same "sun.*" magic on JDK 7 as default java Logger doit)
note static logging methods (with static import) without ugly log property...
import static my.pakg.Logger.*;
And their speed is equivalent to native Java implementation (checked with 1 million of log traces)
package my.pkg;
import java.text.MessageFormat;
import java.util.Arrays;
import java.util.IllegalFormatException;
import java.util.logging.Level;
import java.util.logging.LogRecord;
import sun.misc.JavaLangAccess;
import sun.misc.SharedSecrets;
public class Logger {
static final int CLASS_NAME = 0;
static final int METHOD_NAME = 1;
// Private method to infer the caller's class and method names
protected static String[] getClassName() {
JavaLangAccess access = SharedSecrets.getJavaLangAccess();
Throwable throwable = new Throwable();
int depth = access.getStackTraceDepth(throwable);
boolean lookingForLogger = true;
for (int i = 0; i < depth; i++) {
// Calling getStackTraceElement directly prevents the VM
// from paying the cost of building the entire stack frame.
StackTraceElement frame = access.getStackTraceElement(throwable, i);
String cname = frame.getClassName();
boolean isLoggerImpl = isLoggerImplFrame(cname);
if (lookingForLogger) {
// Skip all frames until we have found the first logger frame.
if (isLoggerImpl) {
lookingForLogger = false;
}
} else {
if (!isLoggerImpl) {
// skip reflection call
if (!cname.startsWith("java.lang.reflect.") && !cname.startsWith("sun.reflect.")) {
// We've found the relevant frame.
return new String[] {cname, frame.getMethodName()};
}
}
}
}
return new String[] {};
// We haven't found a suitable frame, so just punt. This is
// OK as we are only committed to making a "best effort" here.
}
protected static String[] getClassNameJDK5() {
// Get the stack trace.
StackTraceElement stack[] = (new Throwable()).getStackTrace();
// First, search back to a method in the Logger class.
int ix = 0;
while (ix < stack.length) {
StackTraceElement frame = stack[ix];
String cname = frame.getClassName();
if (isLoggerImplFrame(cname)) {
break;
}
ix++;
}
// Now search for the first frame before the "Logger" class.
while (ix < stack.length) {
StackTraceElement frame = stack[ix];
String cname = frame.getClassName();
if (isLoggerImplFrame(cname)) {
// We've found the relevant frame.
return new String[] {cname, frame.getMethodName()};
}
ix++;
}
return new String[] {};
// We haven't found a suitable frame, so just punt. This is
// OK as we are only committed to making a "best effort" here.
}
private static boolean isLoggerImplFrame(String cname) {
// the log record could be created for a platform logger
return (
cname.equals("my.package.Logger") ||
cname.equals("java.util.logging.Logger") ||
cname.startsWith("java.util.logging.LoggingProxyImpl") ||
cname.startsWith("sun.util.logging."));
}
protected static java.util.logging.Logger getLogger(String name) {
return java.util.logging.Logger.getLogger(name);
}
protected static boolean log(Level level, String msg, Object... args) {
return log(level, null, msg, args);
}
protected static boolean log(Level level, Throwable thrown, String msg, Object... args) {
String[] values = getClassName();
java.util.logging.Logger log = getLogger(values[CLASS_NAME]);
if (level != null && log.isLoggable(level)) {
if (msg != null) {
log.log(getRecord(level, thrown, values[CLASS_NAME], values[METHOD_NAME], msg, args));
}
return true;
}
return false;
}
protected static LogRecord getRecord(Level level, Throwable thrown, String className, String methodName, String msg, Object... args) {
LogRecord record = new LogRecord(level, format(msg, args));
record.setSourceClassName(className);
record.setSourceMethodName(methodName);
if (thrown != null) {
record.setThrown(thrown);
}
return record;
}
private static String format(String msg, Object... args) {
if (msg == null || args == null || args.length == 0) {
return msg;
} else if (msg.indexOf('%') >= 0) {
try {
return String.format(msg, args);
} catch (IllegalFormatException esc) {
// none
}
} else if (msg.indexOf('{') >= 0) {
try {
return MessageFormat.format(msg, args);
} catch (IllegalArgumentException exc) {
// none
}
}
if (args.length == 1) {
Object param = args[0];
if (param != null && param.getClass().isArray()) {
return msg + Arrays.toString((Object[]) param);
} else if (param instanceof Throwable){
return msg;
} else {
return msg + param;
}
} else {
return msg + Arrays.toString(args);
}
}
public static void severe(String msg, Object... args) {
log(Level.SEVERE, msg, args);
}
public static void warning(String msg, Object... args) {
log(Level.WARNING, msg, args);
}
public static void info(Throwable thrown, String format, Object... args) {
log(Level.INFO, thrown, format, args);
}
public static void warning(Throwable thrown, String format, Object... args) {
log(Level.WARNING, thrown, format, args);
}
public static void warning(Throwable thrown) {
log(Level.WARNING, thrown, thrown.getMessage());
}
public static void severe(Throwable thrown, String format, Object... args) {
log(Level.SEVERE, thrown, format, args);
}
public static void severe(Throwable thrown) {
log(Level.SEVERE, thrown, thrown.getMessage());
}
public static void info(String msg, Object... args) {
log(Level.INFO, msg, args);
}
public static void fine(String msg, Object... args) {
log(Level.FINE, msg, args);
}
public static void finer(String msg, Object... args) {
log(Level.FINER, msg, args);
}
public static void finest(String msg, Object... args) {
log(Level.FINEST, msg, args);
}
public static boolean isLoggableFinest() {
return isLoggable(Level.FINEST);
}
public static boolean isLoggableFiner() {
return isLoggable(Level.FINER);
}
public static boolean isLoggableFine() {
return isLoggable(Level.FINE);
}
public static boolean isLoggableInfo() {
return isLoggable(Level.INFO);
}
public static boolean isLoggableWarning() {
return isLoggable(Level.WARNING);
}
public static boolean isLoggableSevere() {
return isLoggable(Level.SEVERE);
}
private static boolean isLoggable(Level level) {
return log(level, null);
}
}

Take a look at Logger class from jcabi-log. It does exactly what you're looking for, providing a collection of static methods. You don't need to embed loggers into classes any more:
import com.jcabi.log.Logger;
class Foo {
public void bar() {
Logger.info(this, "doing something...");
}
}
Logger sends all logs to SLF4J, which you can redirect to any other logging facility, in runtime.